1. Field of the Invention
The present invention relates generally to implantable devices and, more particularly, to implantable devices having osseointegrating protuberances.
2. Related Art
Medical devices often include one or more components that are permanently or temporarily implanted in a patient. Many such implantable devices are designed to be mounted adjacent to, abutting, or in the surface of one or more bones. Various techniques have been implemented in order to fix such devices in place and to ensure that the devices do not undergo movement once implanted.
In one conventional approach, an implantable device is the housing for a receiver/stimulator unit has been positioned on a bone within the head of the recipient by drilling a bed or well into and through the posterior section of the mastoid bone lying behind the recipient's ear. Such a bed is usually made by drilling the bone down to the lining of the brain or dura mater, so that the receiver/stimulator unit is maintained in position and does not protrude excessively past the skull surface. The tight dimensions of the bed or well relative to the size of the housing together with the eventual growth of a fibrous capsule serves to help retain the housing in its desired position. One disadvantage of this technique is the time taken in the implant surgery to create the bed. A further disadvantage is that there is some potential for the housing to shift out of the well due to an impact to the head of the recipient. Still further, this technique is not always possible depending upon the thickness of the surrounding bone and the age and anatomy of the recipient.
Another conventional technique has involved the positioning of at least one suture or Dacron tie (bioresorbable or non-bioresorbable) across the housing to hold it in place. (DACRON is a trademark of E.I. du Pont de Nemours and Company) One problem with this approach is that drilling of the holes into the surrounding bone can be a difficult and time consuming procedure, and especially for young children, much care must be taken by the surgeon to ensure that the drilling does not perforate the dura mater, as the skull thickness in such cases can be quite thin. Further to this, the suture or Dacron ties may not be sufficiently strong enough to withstand a substantial impact to a region of the head adjacent the device and as a result, such a force may dislodge the device from its desired position. In addition, it has been found that if a suture or Dacron tie is inadvertently placed across an inappropriate section of the device, such as across a strain relief of the electrode lead, the suture/tie may cause the lead/device to undergo fatigue and cause failure at this location.